U.S. District Judge Terrence Kern struck down the ban, but immediately stayed his ruling pending appeals, the AP reported. The wire service said the judge immediately stayed his ruling pending appeals, meaning gay marriages won't happen in the state right away.

Voters in Oklahoma approved a constitutional amendment in 2004 that says marriage can only be between a man and a woman, AP said. Kern ruled that the measure violates the equal protection clause of the U.S. Constitution by preventing same-sex couples from getting a state marriage licence.

Oklahoma Attorney General Scott Pruitt's office did not immediately comment, the AP reported.